Linking sedimentation rates and large‐scale architecture for facies prediction in nonmarine basins (Paleogene, Almazán Basin, Spain)

Abstract

This article focuses on the relationships between the large‐scale stratigraphic architecture of the Almazán basin infill and the sedimentation rates (SR) calculated for precise time intervals. Our aim was to improve the understanding of the timing and causes of the architectural changes, their significance in terms of accommodation space and sediment supply and their relationship with climate and tectonics. The study area includes the Gómara fluvial fan, the main sediment transfer system of the Almazán basin during Paleogene times. Its large‐scale architecture shifted through time between a stacking pattern of low density ribbon‐like and high density sheet‐like channel fills. Laterally to the fluvial system, mudstone and evaporitic mudstone units represented evaporitic mudflats which passed laterally into palustrine/lacustrine limestone units interpreted as lakes and ponds. Stacked calcretes occurred in distal alluvial and distal floodplain settings. A magnetostratigraphy encompassing 2600 m guided by available fossil mammal biochronology has provided a temporal framework that spans the complete Paleogene infill of the basin, from Late Lutetian to Late Oligocene, filling a gap in the Cenozoic chronostratigraphy of Spanish basins. This permits to constrain the kinematics of the structures both in the basin and in its margins, and to provide the timing for the depositional sequences. These data, combined with a magnetostratigraphic map, where magnetic reversals were traced through the Gómara monocline, allow a detailed analysis of the SR variability across the fluvial system and its adjacent depositional environments. The results show that high sedimentation rates (around 30–40 cm kyr−1) are related to fluvial environments with low density ribbon‐shaped channels, while low SR (around or below 10 cm kyr−1) are related to high density sheet‐like channels. Laterally, mud dominated environments with high SR (15–20 cm kyr−1) grade into palustrine/lacustrine carbonated environments with low SR (around 9 cm ky−1). The lowest SR (about 3 cm kyr−1) are related to the development of stacked calcrete profiles in distal floodplain and in the connection of distal alluvial and palustrine/lacustrine units.

Early stages of clastic deposition in the Most Basin (Ohře Rift, Czech Republic, Early Miocene): timing and possible controls

“…The possibility of tectonic control over depositional sequences is expected in sedimentary basins (Uličný et al 2014, Valero et al 2017. Rajchl et al (2009) assumed that the peat accumulation in the Most Basin was terminated by increased tectonic subsidence and a deposition rate that was several times larger during clastic deposition; however, they did not present a reliable age model that supported their conclusion.…”

“…However, higher sedimentation rates are usually caused by active subsidence that, in turn, generates a less stable sedimentary environment in which local/autogenic forcing may be superimposed on the climatic control. The most robust approach to distinguishing between local and global forcings is to extend the spatial scale of the research by (i) deciphering the basin architecture (Uličný et al , 2014Valero et al …”

“…However, higher sedimentation rates are usually caused by active subsidence that, in turn, generates a less stable sedimentary environment in which local/autogenic forcing may be superimposed on the climatic control. The most robust approach to distinguishing between local and global forcings is to extend the spatial scale of the research by (i) deciphering the basin architecture (Uličný et al , 2014Valero et al 2017) or (ii) comparing sedimentary archives from remote (tectonically independent) areas (Ied et al 2011). In practice, less robust approaches are usually chosen, such as in the Most Basin, in which the sedimentary strata are so monotonous that archival datasets from geological surveys cannot be used and a complete basin analysis is not affordable.…”

Dolomitization, gypsum calcitization and silicification in carbonate–evaporite shallow lacustrine deposits

“…The DF mainly consists of limestones, dolostones and marls. Its age is Upper Eocene on the basis of magnetostratigraphy (Valero et al, 2015). During deposition of the DF, only the Mesozoic outcrops sourced the eastern part of the basin (Huerta, 2007;Valero et al, 2015).…”

“…Its age is Upper Eocene on the basis of magnetostratigraphy (Valero et al, 2015). During deposition of the DF, only the Mesozoic outcrops sourced the eastern part of the basin (Huerta, 2007;Valero et al, 2015). The top of this formation is a depositional sequence boundary that marks a tectonic pulse followed by a large input of conglomerates derived from Palaeozoic rocks.…”